While saliva obtained from HIV positive subjects is often PCR positive for HIV RNA sequences, it is extremely difficult to culture virus from oral samples. Coupled with the epidemiologic observations that HIV is rarely orally transmitted, it is now widely believed that saliva contains factors that inactivate the virus. We previously demonstrated that saliva from most individuals was able to specifically inhibit HIV-1 infection in vitro. Submandibular and parotid saliva samples from individuals demonstrating high levels of anti-HIV activity were used to identify and then purify two high molecular weight sialyated glycoproteins, salivary agglutinin (SAG) and mucin (MG2). Both of these purified glycoproteins inhibited HIV-1 infection in vitro at concentrations found in saliva. We subsequently demonstrated that the mechanism of inhibition involved binding of the salivary proteins to gp120, and subsequent shedding of gp120 from the virion. Prakobphol et al (2000), utilizing proteomic technology, demonstrated that SAG was identical to the lung scavenger receptor protein, gp-340, a member of the scavenger receptor cysteine rich (SRCR) family. We obtained a molecular clone for this gene, expressed the protein in mammalian cells and found that recombinant gp-340 was identical to SAG in terms of its structural and biologic activities. In the present proposal we will (1) Identify regions on gp120 that interact with gp-340; create stable transfected cells that express high levels of gp-340, and demonstrate that it is indeed identical to SAG in all of its biologic properties; (2) Identify discrete regions of gp-340 that mediate env binding and HIV inhibition; and (3) establish the mechanism(s) involved in the interaction of the bioactive portion of gp-340 in order to develop novel therapeutic agents with anti-HIV activity.